The present disclosure relates to an inkjet recording apparatus which performs recording by discharging ink onto a recording medium such as paper in a recording apparatus such as a facsimile machine, copier, or printer, and relates in particular to recovery of a recording head which discharges ink.
A recording apparatus such as a facsimile machine, copier, or printer is configured to record an image on a recording medium such as paper, cloth, or OHP sheet. Depending on the method used for recording, a recording apparatus is classified into an inkjet type, a wire dot type, a thermal type, etc. An inkjet recording method can be further classified into a serial type, where recording is performed while a recording head scans across a recording medium, or a line head type, where recording is performed by a recording head fixed to the apparatus body.
In such an inkjet recording apparatus, with respect to discharge nozzles on standby for printing or between sheets during continuous printing, or discharge nozzles that remain unused during printing, no cap is attached. In addition, in a discharge nozzle that goes without discharging ink, moisture keeps evaporating from the ink inside it, and the ink comes to have increased viscosity. As a result, when the nozzle is later expected to discharge ink, inconveniently, it may discharge ink improperly or even fail to discharge ink.
In particular, in a line head recording method where a recording head is fixed, each nozzle of the recording head corresponds to one particular pixel (dot) in one line of an image. Thus, some nozzles, such as those corresponding to pixels in the left and right margins, go without discharging ink even once during printing of one image. These nozzles may later have to form dots for different image data, and therefore need to stay ready to discharge ink stably whenever actuated.
In a widely adopted design, discharge nozzles, which have openings on the ink discharge surface of a recording head, are prevented from ink dryout and ink clogging through a recording head recovery process which involves forcing ink out of the nozzles (purging) and then wiping off the ink deposited on the ink discharge surface (wiping). Inconveniently, through this process, a large amount of ink is dumped without being used, and is thus wasted. Moreover, forcible discharge is performed not only for nozzles that have not discharged ink but also for nozzles immediately after ink discharge. This is inefficient.
On the other hand, as a recording head for an inkjet recording apparatus, a piezoelectric inkjet head is widely used. In a piezoelectric inkjet head, the force produced by a piezoelectric element is transmitted, as a pressure, to ink inside a pressurizing chamber so that the pressure makes the ink meniscus inside a nozzle swing for generating ink droplets.
Thus, according to a conventionally proposed method, the ink meniscus inside a nozzle is oscillated in such a degree as not to discharge ink, with the aim of preventing nozzle clogging. However, such meniscus swinging stirs the ink inside the nozzle; thus, ink near the meniscus with increased viscosity due to evaporation of moisture is diffused deeper in the nozzle, and instead ink with no increase in viscosity moves toward the meniscus. Here, compared with ink with increased viscosity, which is short of moisture, ink with no increase in viscosity allows moisture to evaporate faster. Thus, ink near the meniscus tends to show a faster increase in viscosity.
As discussed above, performing meniscus swinging for a nozzle that does not form a dot even once within one sheet-worth image data contrarily prompts an increase in the viscosity of ink inside the nozzle, causing gradual degradation of ink dischargeability. Thus, after switching to image data for printing on the subsequent sheet, when a dot is formed by use of a nozzle that has formed no dot on the previous sheet, ink droplets may be discharged improperly.
In a conventionally known inkjet recording apparatus, ink with increased viscosity inside the nozzle is discharged with the aim of preventing ink clogging; that is, preparatory discharge (waste printing) is performed. In this inkjet recording apparatus, preparatory discharge is performed on paper, and thus there is no need to wipe the ink discharge surface of the recording head.